《ASP.NET Core技术内幕与项目实战》精简集-高级组件4.4：消息推送SignalR

//第一步：在Hubs文件夹中，创建集线器类
//ChatRoomHub.cs，继承自Hub类
public class ChatRoomHub : Hub 
{
    //集线器方法，客户端可以请求调用
    public Task SendPublicMessage(string user, string message)
    {
        string connId = Context.ConnectionId; //获取连接客户端ID
        string msg = $"{connId}/{user}: {message}";
        //向所有连接的客户端发送消息，消息名“ReceivePublicMessage”，消息内容msg
        return Clients.All.SendAsync("ReceivePublicMessage", msg);
    }
}


//第二步：配置SignalR服务
//program.cs
var builder = WebApplication.CreateBuilder(args);
......
//注册SignalR服务
builder.Services.AddSignalR();

//注册跨域服务，并将Blazor项目的URL设置为可信任
string[] corsUrls = new[] { "https://localhost:7042", "http://localhost:5042" };
builder.Services.AddCors(opts =>
{
    opts.AddDefaultPolicy(builder =>
    {        builder.WithOrigins(corsUrls).AllowAnyMethod().AllowAnyHeader().AllowCredentials();
    });
});

var app = builder.Build();
......
//启用跨域中间件
app.UseCors();

app.UseHttpsRedirection();
......
//启用和配置SignalR中间件，当客户端访问/Hubs/ChatRoomHub时，使用ChatRoomHub进行处理
app.MapHub<ChatRoomHub>("/Hubs/ChatRoomHub");

app.MapControllers();
app.Run();

//第一步：安装Nuget包，Microsoft.AspNetCore.SignalR.Client


//第二步：创建前端UI，模拟简单的聊天室，在同一页面，发送消息和接收消息
//Index.razor
<h3>User:</h3><input @bind = "userInput" />
<h3>Message:</h3><input @bind = "messageInput" />
<button @onclick = "Send" disabled="@(!IsConnected)">发送</button>
@foreach (var message in messages)
{
    <li>@message</li>
}

@code{
    private HubConnection? hubConnection; //集线器连接对象
    private string? userInput; //输入用户名
    private string? messageInput; //输入聊天信息
    private List<string> messages = new List<string>(); //聊天记录
    
    protected override async Task OnInitializedAsync()
    {
        //创建集线器连接
        hubConnection = new HubConnectionBuilder()
            .WithUrl("https://localhost:7110/Hubs/ChatRoomHub")
            .WithAutomaticReconnect()
            .Build();
        
        //监听集线器消息，将消息内容添加到messages集合中，并刷新
        hubConnection.On<string>("ReceivePublicMessage", msg =>
        {
            messages.Add(msg);
            StateHasChanged();
        });

        //开始连接集线器
        await hubConnection.StartAsync();
    }

    //如果已连接集线器，则调用集线器方法，发送信息
    private async Task Send()
    {
        if (hubConnection is not null)
            {
                await hubConnection.SendAsync("SendPublicMessage", userInput, messageInput);
            }
    }

    //判断客户端是否连接集线器
    public bool IsConnected =>
        hubConnection?.State == HubConnectionState.Connected;
    
    //组件销毁时，断开集线器连接（销毁集线器连接对象）
    public async ValueTask DisposeAsync()
    {
        if (hubConnection is not null)
        {
            await hubConnection.DisposeAsync();
        }
    }
}

//第一步：服务端，在控制器中注入IHubContext<THub>服务，并发送消息
[Route("api/[controller]/[action]")]
[ApiController]
public class MyController : ControllerBase
{
    private readonly IHubContext<ChatRoomHub> hubContext;
    public MyController(IHubContext<ChatRoomHub> hubContext)
    {
        this.hubContext = hubContext;
    }

    [HttpGet]
    public async Task<ActionResult> SendControllerMessage(string msg)
    {
        await hubContext.Clients.All.SendAsync("ControllerMessage", msg);
        return Ok();
    }
}


//客户端，在前端中增加对消息“ControllerMessage”的监听
hubConnection.On<string>("ControllerMessage", msg =>
{
    messages.Add(msg);
    StateHasChanged();
});

//客户端连接时，禁止协商设置
hubConnection = new HubConnectionBuilder()
    .WithUrl("https://localhost:7110/Hubs/ChatRoomHub",options =>
    {
        options.SkipNegotiation = true;
        options.Transports = HttpTransportType.WebSockets;
    })
    .WithAutomaticReconnect()
    .Build();

//AddStackExchangeRedis方法的第一个参数为Redis服务器地址，第一个参数配置当前应用程序的前缀
builder.Services.AddSignalR().AddStackExchangeRedis("127.0.0.1", opts =>
{
    opts.Configuraton.ChannelPrefix = "Test1_"
});